In a hybrid driving apparatus having an engine and an electric motor as a driving sources, a torque fluctuation absorbing apparatus is provided at output shafts of the engine or/and the electric motor. The torque fluctuation absorbing apparatus is adjusted to absorb or damp fluctuations in the torque generated by the engine and the electric motor. JP2005-127507A discloses therein a torque fluctuation absorbing device including a first rotational member transmitted with a torque from a driving power source, a damping mechanism connected to an input shaft of a transmission and having frictional members of an approximately annular-shaped fixed at both surfaces of a disc, and a limiter portion frictionally engaging the frictional members with the first rotational member in a direct manner or in an indirect manner via frictional plates. In this torque fluctuation absorbing device, each of the frictional members has, on its frictional surface, a non-frictional area at a ratio of substantially between 20 percent and 80 percent (inclusive 20 and 80 percents) relative to the entire area of the frictional surface. The non-frictional area may be a groove. The frictional member is adhered to a disc and includes a reinforcing material which is more rigid than the frictional member, thereby increasing rigidness of the frictional member. The reinforcing material is generally reinforcing fibers.
However, a vicinity of such reinforcing fiber exhibits high absorbency and low rust-resistance. Therefore, an occurrence of rust caused by water invasion may unnecessarily lead a slip torque of the limiter portion to more than a predetermined torque.
Further, although the above-described torque fluctuation absorbing apparatus includes a groove formed in the frictional member, the groove is formed to reduce deterioration with age, which deterioration occurs due to a slidable movement of the frictional material. In other words, the groove needs to be considered if it is appropriate in terms of rust-resistance.
Still further, in the above-described torque fluctuation absorbing apparatus, the frictional member is adhered to the disc, which increases a manufacturing cost. Moreover, the adhesion requires a long processing time and a preparation in advance. The frictional member may be secured to disc by a conventionally known riveted structure such as a clutch at a lower manufacturing cost, and however the following matter still remain to be improved.
First of all, an increase in the ratio of the reinforcement fiber included in the frictional member, which leads to reinforcement of the frictional member, introduces occurrences of rusts. Secondarily, the frictional member is generally drilled to be caulked. In this case, the reinforcement fiber may be cut unfavorably and the rigidness of the frictional member is deteriorated. Thirdly, the width (the difference between the inner diameter and the outer diameter) and the thickness of the frictional member may be increased. This increases a space and cost required to the frictional member. Fourthly, the increase in the width of the frictional member may advance deterioration with age of the frictional member slidably movable.
A need thus exists for a torque fluctuation absorbing apparatus which is not susceptible to the drawback mentioned above.